Numerical Simulation Study On Enhancement Of Graphite Foam To Eutectic Salt Phase Change Thermal Storage

Nowadays, the issue of energy conservation and environmental protection has gained increasingly attention worldwide. Energy shortage and environmental pollution which caused by excessive energy consumption are becoming more and more serious. Under the pressure of environment and resources, the solar focus of thermal power generation (CSP) is the most promising power way except wind energy source power generation as a renewable technology. CSP is the technology which collect solar energy and transfer it into high temperature thermal energy of working fluid, and then convert it into electrical energy. Due to the unstabitily of solar energy supply, a energy storage system which absorb solar energy and convert it into electrical energy continuously is required to ensure steady running of solar energy power generation system.But the thermal conductivity of phase change materials used in this system was very small, which has affected the rate of heat release and storage, so approaches is needed to enhance the effective transfer rate of phase change.In this paper, we used commercial software Fluent to investigate the performance of heat transfer enhancement for graphite foam with porosity of 0.728 on phase change material (eutectic salt), and analyze the influence of graphite foam and other parameters on phase change process, and this would provide a guideline for solar focus of thermal power generation. The main contents and results of the paper are described as follows:1) Established and simplified mathematical and physical model; conducted the model validation by comparing the computed results with experimental data of literature, and assured the accuracy of model used in this paper; then checked the independence for grids.2) Phase change processes of graphite foam/eutectic salt materials and pure eutectic salt had been studied, and results showed that effective thermal conductivity of graphite foam/eutectic salt is 41.164 W/(m·K), and improve 40.664 W/(m·K) compare with pure eutectic salt.3) Analysed the parameters in phase change process of graphite foam/ eutectic salt and pure eutectic salt respectively,results showed that the heat transfer rate increased greatly, time of phase change reduced because of the existence of graphite foam, but the total heat storage reduced a little; the beginning time of phase change lagged behind and temperature distribution and phase interface distribution varied for graphite foam/ eutectic salt system compare with pure eutectic salt system.4) Influence of heat flux(q) on phase change of graphite foam/eutectic salt system had been analyzed, results showed that heat transfer rate improve with the increase of heat flux in a certain range. Relationship between melting time and heat flux is t=505911g-0.991 and formula of time for solidification process describe as t=519.69e0.0003q.5) Investigated the influence of natural convection on phase change process of pure eutectic salt and graphite foam/eutectic salt system respectively and found that influence of natural convection on melting process was more obvious;the existence of graphite foam weakened the natural convection.6) Dimensions of phase change system model for graphite foam/eutectic salt was analysed and the results showed relationship between heat exchange tube D、radius of tube r and melting time, the formula represent as t=0.005D3.3404 and t=114.09r-0.1531 respectively.7) Analyzed the influence of porous medium resistance on the phase transition process for graphite foam/eutectic salt system; then the influence of porosity on phase change process was researched,equation of melting time-porosity(η) and effective thermal conductivity(κ)-porosity(η) were obtain as t=2027.1η2-3003.6η+1208.2 andκ=150-149.5η; compared the changes of effective thermal conductivity and total energy with porosity, and got a balance porosity 0.87.